The worst environmental disaster in American history is the subject of a trial that is beginning today. It's a big and complicated civil lawsuit stemming from the 2010 explosion of the Deepwater Horizon oil rig in the Gulf of Mexico - and, of course, the spill that followed that.

We're going to talk about this with two NPR correspondents who've been covering this story for years. The first is NPR's Debbie Elliott. She's on the Gulf Coast. Debbie, Good morning.

DEBBIE ELLIOTT, BYLINE: Morning, Steve.

INSKEEP: You know, this oil spill - which captivated all of us in 2010 - is starting to feel rather distant in time. Does it feel like a long-ago event, though, on the Gulf of Mexico?

ELLIOTT: Certainly not for the people on the Gulf and who live along the Gulf Coast. You know, a lot of people have seen these ads that BP has been running that say come back to the Gulf. We've cleaned everything up, and everything is great. And the reality is, is that there are still 200 miles of oiled shoreline in Louisiana, for example, wetlands that are still covered in oil. The reality on the Alabama Gulf Coast is that every time there's a thunderstorm or a hurricane or a tropical storm or the surf gets turned up, there are tar mats that are submerged out in the Gulf of Mexico, and that surf churns up those tar mats, and tar balls come back on the beach and have to be cleaned up again. So this is an ongoing event that people have been living with for nearly three years now.

INSKEEP: OK. So this is a story that has faded a little bit from national attention, but is still happening where Debbie Elliott is. And let's bring in now NPR's Carrie Johnson, our justice correspondent. She covers the Justice Department. And let's talk about the case here, Carrie. What does the government have to prove in order to get BP to pay up billions of dollars in damages?

CARRIE JOHNSON, BYLINE: One of the central questions in this trial is whether BP engaged in gross negligence, causing - or helping to cause - an explosion that led to the fouling of the Gulf in April 2010. And BP, as you may remember earlier this year, has admitted to a criminal charge. But BP is still going to argue that it made some mistakes, but the blame should be shared with its contractors, like Halliburton and Transocean, the owner of that Deepwater Water Horizon rig. The Justice Department says it intends to prove that BP acted with recklessness and willful disregard for the safety of workers.

Remember, Steve, 11 people died on that rig. And the Justice Department says through expert witness testimonies, emails from BP officials in which they talk in the days before the spill about flying by the seat of their pants, that they were putting profits over employee safety. That's a huge question worth a huge amount of money, because if the Justice Department can only prove that BP engaged in simple negligence, BP is on the hook for about four-and-a-half billion dollars.

INSKEEP: A lot - but?

JOHNSON: A lot - but almost four times as much if the Justice Department can prove that BP engaged in gross negligence.

INSKEEP: Well, let me just ask: Is it surprising at all to either of you that this has come to trial, rather than BP simply settling out of court, as so often happens with civil lawsuits?

ELLIOTT: You know, I think a lot of observers did expect that this would likely settle, because BP has settled a lot of other cases. They settled with private plaintiffs, the individuals and businesses who were harmed by the oil spill economically and who might have medical claims. BP agreed to pay at least $7.8 billion - could be higher - to cover those claims. BP has admitted its role in the accident and settled criminal charges with the Justice Department.

But last week, we heard BP general counsel Rupert Bondy say the company had been faced with demands that were excessive and not based on reality. And we think that those demands are coming mostly from the states. The two lead states in this litigation, Alabama and Louisiana, have said they are not willing to agree to any settlement unless BP pays enough to cover any long-term damage to the Gulf, damage that we may not know about right now.

INSKEEP: Well, let me ask about that, because when the still happened, it seemed like just an unimaginably bad event. Then there was a round of stories some months later about how maybe the oil spill was not that devastating after all. A lot of the oil seemed to have vanished. Now, Debbie Elliott, you're telling us that years later, oil is still washing ashore. How long is it going to take before we know the true scope of the devastation here?

ELLIOTT: You know, some people will say it could take 10 years, 20 years. Nobody really can answer that question.

JOHNSON: That's right. Many environmental groups and many government scientists are trying to figure that out right now, and it has a huge implication for how much BP must ultimately pay under violations of the Oil Pollution Act.

INSKEEP: Carrie Johnson, thanks very much.

JOHNSON: Thank you.

INSKEEP: She's NPR's justice correspondent. And NPR's Debbie Elliott will be covering the civil trial against BP in New Orleans. Debbie, thanks to you.